Method and program for manufacturing a product having locally specific properties

ABSTRACT

A method for manufacturing a product having locally specific properties, the geometric form of which is described by a collection of polygonal basic figures in particular in STL (structural triangulation language), comprises the following steps: selecting the above basic figures a face part composed of coherent basic figures, adding to that face part at least one specific property, which during the manufacture of the product is to be given to the part thereof that comprises the above face part, optionally repeating the above process steps for other face parts to be selected, and manufacturing the product on the basis of the then obtained model information by means of a technique adding material in layers or in a die molding process, which includes giving the associated specific property during the building up in layers of at least the part of the product that comprises the above face part or during the injection molding.

BACKGROUND OF THE INVENTION

The present invention relates to a method for manufacturing a producthaving locally specific properties, the geometric form of which isdescribed by a collection of polygonal basic figures, in particular inSTL (structural triangulation language).

Such products can be manufactured by building up the product in layersby using all kinds of techniques adding material in layers, known underthe designation LMT (layers manufacturing technology) or SFF (solidfreedom fabrication), such as, for instance, stereolithography andselective laser sintering. It is also possible to manufacture suchproducts in a die molding process, in which connection the term die isalso understood to mean all types of punches and further tools that arenecessary for manufacturing specific product forms. When designing andmanufacturing such products, CAD/CAM systems are often used. It shouldbe noted that a product built up in layers may also include a die which,in turn, can be used for manufacturing a further product having locallyspecific properties.

SUMMARY OF THE INVENTION

In order to give in these known techniques the product to bemanufactured a greater flexibility in appearance, material compositionand/or physical or other properties, the method as described in theopening paragraph comprises according to the invention the followingsteps: selecting from the above basic figures a face part composed ofcoherent basic figures, adding to that face part at least one specificproperty, which during the manufacture of the product is to be given tothe part thereof that comprises the above face part, optionallyrepeating the above process steps for other face parts to be selected,and manufacturing the product on the basis of the then obtained modelinformation by means of a technique adding material in layers or in adie molding process, which includes giving the associated specificproperty during the building up in layers of at least the part of theproduct that comprises the above face part or during the injectionmolding.

The above specific properties can relate to the color to be given tospecific face parts, the material composition of specific parts of theproduct and/or the physical or other properties of specific parts of theproduct, such as the elasticity, the hardness and the like, or, when themethod is used in a die molding process, the designation of the part ofthe product to be manufactured in a specific die half. When the productis a die, for instance a technique adding material in layers can be usedfor manufacturing parts of a die half from different materials. In thismanner, different parts of the die can be given different properties,such as, for instance, a different heat conductivity, or the die can belocally provided with a wear-resistant layer in one operating cycle.

Moreover, several properties can be assigned to face parts, for instanceboth a specific material composition and a color. Adding specificproperties to a face part means both directly assigning specificproperties to the basic figures of the face part and indirectlyassigning specific properties to the basic figures of the face part byassigning these properties to the face part, after which they are addedto the basic figures which this face part is composed of.

The wall thickness of the face parts which together set up the model iszero, for which reason, after one or more specific properties have beengiven to one or more selected face parts, the model information thenrelating to a shell model (having wall thickness zero) will be convertedinto model information relating to a volumetric model, after which onthe basis of the latter information the product is manufactured by meansof a technique adding material in layers. Of course, this measure is notapplicable in a die molding process. In fact, a CAD model, in whichspecific properties have been added to the basic figures, remains a CADmodel that can be directly supplied to a CAM system.

Selecting face parts can occur by displaying the geometric form of theproduct on the screen of a monitor belonging to a computer, indicating apolygonal basic figure on the monitor, after which all these basicfigures are combined with the indicated basic figure to a face part, thenormal vectors of which mutually or relative to the normal vector of theindicated basic figure do not exceed a preset angular difference.

Adding the face parts of specific properties can occur by selecting acode from the specific properties stored in code in the memory of acomputer and adding them to file data belonging to the selected faceparts. This code can be stored for each of the basic figures in thememory of the computer.

When the basic figures consist of triangles in STL, the code can bestored for each of the triangles in the memory space available in theSTL file of each triangle. The standard available memory space ispresently two bytes, so that for instance in the memory space availablein the STL file of each triangle 2¹⁵ color codes can be stored.

The invention further relates to a computer program used formanufacturing a product having locally specific properties, thegeometric form of which is described by a collection of polygonal basicfigures, in particular in STL (structural triangulation language), whichprogram comprises the following steps: selecting from the above basicfigures a face part composed of coherent basic figures and adding tothat face part at least one specific property, which during themanufacture of the product is to be given to the part thereof thatcomprises the above face part, optionally repeating the above processsteps for other face parts to be selected. The program can be used formanufacturing products both by means of a technique adding material inlayers and in a die molding process. Specifically when using the formertechniques, the program is of such design that, after one or morespecific properties have been given to one or more selected face parts,the model information then relating to a shell model is converted intomodel information relating to a volumetric model, after which on thebasis of the latter information the product can be manufactured by meansof a technique adding material in layers.

Finally, the invention relates to a computer system used during themanufacture of a product having locally specific properties, thegeometric form of which is described by a collection of polygonal basicfigures, in particular in STL (structural triangulation language), whichcomputer system uses one of the above systems.

The invention will now be explained in more detail with reference to theaccompanying drawing. In this drawing:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block-shaped model in STL having in relief thereon aletter T to be designed in another color than the block itself;

FIG. 2 shows a part of the letter T in FIG. 1, but in which thetransition from the top face of the letter to the background is notsharp; and

FIG. 3 shows a cross-section of the part of the letter T shown in FIG.2.

FIGS. 4A-C show succession of a shell model of a cube-shapes object;

FIGS. 5A-C show triangles in colored triangulation language (CTL);

FIG. 6 shows a flow diagram for the method of the present invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Although a geometric form can be described by a collection of polygonalbasic figures in general, triangular basic figures will be started fromhereinbelow, i.e. basic figures in standard STL (structuraltriangulation language), such as provided by a CAD system, for instancewhen using a “rapid prototyping technique”. The STL file comprises acollection of triangles, each of which is described by three coordinatesand a normal vector. Besides, per triangle two bytes are presentlystandard available for additional information. In the example describedwith reference to FIG. 1 this information will consist of a color code.FIG. 1 shows a block-shaped model in STL having in relief thereon aletter T to be designed in another color than the block itself. In orderto be able to give each triangle a color code, the object, in thisexample the block-shaped model of FIG. 1, is displayedthree-dimensionally on the screen of a monitor belonging to a computer.Then a triangle, for instance triangle 1, is indicated on the screenwith the cursor. This is followed by automatically selecting all thealways adjacent triangles that satisfy a preset criterion, that is tosay that the angle between the normal vectors, also referred to astolerance angle, of the always adjacent triangles must be smaller than apredetermined value. If in the example described here this toleranceangle is 60°, then, after indication of triangle 1, the triangles 2, 3and 4 will be directly selected. By then selecting a desired color froma color code stored in the memory, the relevant code is added to the STLfiles of the triangles 1-4. Then background triangle 5 is to beindicated in this example, after which, by using the same criterion, thetriangles 6-16 will be directly selected. Moreover, a color code can beadded to the STL files of this group. After that this process can berepeated until a color code has further been added to the STL files ofthe triangles in all the vertical faces of the model shown in FIG. 1. Inthis manner, groups of triangles, that is to say face parts, areobtained, of which, for the relevant triangles, a color code is includedin the STL files. Thus, for instance, the block in FIG. 1 can be giventhe color white, and the letter T provided thereon in relief can begiven the color red. If in this example a tolerance angle of, forinstance, 100° is selected as criterion for the vertical faces of theletter T and of the block, then, after a triangle has been indicated ina relevant vertical face, all the triangles in all the vertical faces ofthe letter T or of the block can be selected in one go. This, however,is only possible if the face parts already provided with a color codeare excluded.

Problems can occur when the transition between two face parts is notsharp enough. This situation is shown in FIGS. 2 and 3. FIG. 2 shows apart of the letter T in FIG. 1, but in which the transition from the topface of the letter to the background is not sharp, while FIG. 3 shows across-section of the part of the letter T shown in FIG. 2. In FIG. 2 thetriangular structure is only shown in one of the transition faces fromthe upwardly projecting relief face to the background face. If thetolerance angle between two adjacent triangles is always considered,then, after for instance indicating the upper triangle 17, all thetriangles in the relevant transition face will be selected successively.It is also possible, however, to always compare the normal vectors ofthe relevant triangles with those of the triangle 17, so that, if anangle between the normal vectors of for instance 30° is taken ascriterion, only the upper group of triangles is selected. This can bereferred to as a relative tolerance angle in the first case and as anabsolute tolerance angle in the second case.

Moreover, it is possible to display the cross-section on the screen(FIG. 3) and, by providing a window, to indicate the parts 18 of therelevant transition faces to which a specific color code is to be added.

By adding a color code in the STL files of the model, this is describedin CTL (colored triangulation language). A CAD model in CTL can besupplied to a CAM system for designing a die, after which the productscan be manufactured by means of a correspondingly realized die byinjection molding, in which connection the color in which specific partsof the product are to be molded must be considered. In the example shownin FIG. 1, for instance, the block can be formed in one die half and theletter T in the other die half. By introducing a white plastic of forinstance ABS (acrylonitrile-butadiene-styrene copolymer) into the diefrom one die half and, if this is sufficiently hardened, a red plasticof for instance PC (polycarbonate) from the other die half, a productsprayed in two colors can be obtained. The die, however, must then bedesigned in an appropriate manner.

In order to be able to manufacture a product in a technique addingmaterial in layers, a model shown in CTL is insufficient. In fact, thewall thickness of the face parts which together set up the model iszero; such a model is further indicated as shell model. This shell modelmust be converted into a volumetric model.

After the face parts to be given a specific color have been selected, aconversion of the shell model built up by the common face parts into avolumetric model must take place. Successively shown in FIGS. 4A-4C area shell model of a cube-shaped object, a solid element model thereof anda solid element shell model of this object. Assuming the face partsformed by the four upright sides have been given the color codes blue(Bl), red (Re), green (Gr) and yellow (Ye), then the model 4A describedin CTL must be converted into a volumetric model, that is to say ineither the solid element model 4B or the solid element shell model 4C.In fact, a so-called “slice” can be made from these models 4B and 4C,that is to say a layer having an indicated thickness. The product canthen be built up in a manner known for techniques adding material inlayers by providing layers 19 on each other (FIG. 4C), while thedifferent parts of each layer are provided in the indicated color.

The method in which a model in STL is converted into CTL, and ifrequired subsequently into a volumetric model, is realized by means of aprogram appropriate therefor. The algorithm must then be such that thefaces to be extruded do not intersect each other. In FIG. 5A threetriangles are shown in CTL. If a solid element shell model is madetherefrom without anything more, a product as shown in FIG. 5B will beobtained. Corrections in the algorithm must ensure that a model as shownin FIG. 5C is obtained. Of course, other corrections can also be made,if so desired.

The invention is not limited to the exemplary embodiments describedherein with reference to the Figures, but comprises all kinds ofmodifications thereof, of course as far as falling within the scope ofprotection of the appended claims.

Thus, for instance, it is possible that the codes to be added to themodel in STL not only relate to the color of selected face parts, butalso to other specific properties or to combinations of specificproperties, as already mentioned before. Thus, for instance, the uprightred and yellow side faces of the solid element shell model shown in FIG.4C can be manufactured from a harder plastic than the blue and greenupright side faces.

The method described herein is realized by means of computer programsspecifically directed to selecting from the basic figures a face partcomposed of coherent basic figures and adding to that face part at leastone specific property, which during the manufacture of the product is tobe given to the part thereof that comprises the above face part, andoptionally repeating these process steps for other face parts to beselected, or to converting the model information then relating to ashell model into model information relating to a volumetric model.

1. A method for manufacturing a product having locally specificproperties, the geometric form of which is described by a collection ofpolygonal basic figures, in particular in STL (structural triangulationlanguage), the method comprises the following steps: selecting from thecollection of polygonal basic figures a subset of basic figuresdescribing a coherent part of a surface of the product, the basicfigures in the subset being selected automatically by selecting basicfigures that are always adjacent to at least one previously selectedbasic figure from the surface part, so that the part of the surfacedefined by the selected basic figures is coherent, after the selectingstep, assigning to the subset at least one specific property, whichduring the manufacture of the product is to be given to the part thereofthat comprises said coherent part of the surface, optionally repeatingthe above process steps for other coherent part of the surface to beselected, and manufacturing the product on the basis of the thenobtained model information by means of a technique adding material inlayers or in a die molding process, which includes giving the associatedspecific property during the building up in layers of at least the partof the product that comprises the coherent part of the surface or duringthe injection molding.
 2. The method according to claim 1, wherein,after one or more specific properties have been given to one or moreselected coherent parts of the surface, the model information thenrelating to a shell model is converted into model information relatingto a volumetric model, after which on the basis of the latterinformation the product is manufactured by means of a technique addingmaterial in layers.
 3. The method according to claim 1, whereinselecting coherent parts of the surface occurs by displaying thegeometric form of the product on a computer monitor, indicating apolygonal basic figure on the monitor, after which all the basic figuresare combined with the indicated basic figure to a coherent part of thesurface the normal vectors of which mutually or relative to the normalvector of the indicated basic figure do not exceed a present angulardifference.
 4. The method according to claim 1, wherein adding specificproperties to the coherent part of the surface occurs by selecting acode from the specific properties stored in code in the memory of acomputer and adding them to file data belonging to the selected faceparts.
 5. The method according to claim 4, wherein the specificproperties art selected from the following properties including thecolor of a face part, the physical properties of a face part, such asthe material composition, and the indication of the part of a productthat is to be manufactured in a specific die half.
 6. The methodaccording to claim 4, wherein the above code is stored for each of thebasic figures in a computer memory.
 7. The method according to claim 4,wherein the basic figures include triangles in STL, and wherein the codeis stored for each of the triangles the memory space available in theSTL file of each triangle.
 8. The method according to claim 7, wherein2¹⁵ color codes are capable of being stored in the memory spaceavailable in the STL file of each triangle.
 9. A product producedaccording to the process of claim
 1. 10. A product having locallyspecific properties including a geometric form described by a collectionof polygonal basic figures in STL (structural triangulation language)produced by performing the steps of: selecting from the collection ofpolygonal basic figures at let one part of a surface composed ofcoherent basic figures; and adding to the coherent part of the surfaceat least one specific property, which during the manufacture of theproduct is to be given to the part thereof that comprises the coherentpart of the surface, optionally repeating the above process steps forother coherent parts of the surface to be selected, and manufacturingthe product on the basis of the then obtained model information by meansof a technique adding material in layers or in a die molding processwhich includes giving the associated specific property during thebuilding up in layers of at least the part of the product that comprisesthe coherent part of the surface or during the injection molding. 11.The product according to claim 10, wherein the producing steps furthercomprise: after one or more specific properties have been given to oneor more selected coherent part of the surface, model informationrelating to a shell model is converted into model information relatingto a volumetric model, after which on the basis of the latterinformation the product is manufactured by means of a technique addingmaterial in layers.
 12. A system for manufacturing a product havinglocally specific properties including a geometric form described by acollection of polygonal basic figures, in particular in STL (structuraltriangulation language), the system comprising: means for selecting fromthe basic figures a coherent part of the surface composed of coherentbasic figures, and adding to the coherent part of the surface at leastone specific property, which during the manufacture of the product is tobe given to the part thereof that comprises the coherent pant of thesurface, and means for optionally repeating the above process steps forother coherent parts of the surface to be selected.
 13. The system ofclaim 12, wherein the means for selecting, after one or more specificproperties have been given to one or more selected coherent part of thesurface, converts model information relating to a shell model into modelinformation relating to a volumetric model, such that on the basis ofthe latter information the product is capable of being manufactured bymeans of a technique adding material in layers.